Abstract: Systems and methods for sensing changes in an optical sensing fibre, principally for detecting changes in strain. A plurality of optical probe pulses at different optical frequencies (f1, f2, . . . fn) spaced by ?f are transmitted into the sensing fibre. Light backscattered from the optical sensing fibre may be mixed with delayed backscatter frequency shifted by ?f+fm where fm is a heterodyne frequency. The backscattered or mixed light may be detected to determine changes in the sensing fibre. ?f may be chosen to optimise performance.

Abstract: Systems and methods for sensing changes in an optical sensing fibre, principally for detecting changes in strain. A plurality of optical probe pulses at different optical frequencies (f1, f2, . . . fn) spaced by ?f are transmitted into the sensing fibre. Light backscattered from the optical sensing fibre may be mixed with delayed backscatter frequency shifted by ?f+fm where fm is a heterodyne frequency. The backscattered or mixed light may be detected to determine changes in the sensing fibre. ?f may be chosen to optimise performance.

Abstract: An optical monitoring system comprising first and second sensor arrays interrogated via first and second optical connections from an interrogator location. The system is configured such that no wavelength is carried bi-directionally in the first and second optical connections. In typical systems the optical connections comprise trunk cables from the sensor arrays to the interrogator location.

Abstract: An optical monitoring system comprising first and second sensor arrays interrogated via first and second optical connections from an interrogator location. The system is configured such that no wavelength is carried bi-directionally in the first and second optical connections. In typical systems the optical connections comprise trunk cables from the sensor arrays to the interrogator location.

Abstract: A sensor arrangement for monitoring a oil reservoir comprises a sensor array (1) comprising a plurality of sensor units (5) located over an area to be monitored; an interrogator unit (30) comprising a transmitter (402) for transmitting optical signals and receiver for obtaining data on the reservoir from the sensor units, a demodulator (418) for demodulating the received signals, and a recorder (420) for recording the demodulated signals. The arrangement includes an uplink optical cable (408) for transmitting the signals to the sensor array and a downlink optical cable (410) for transmitting signals from the array to the receiver. At least one of the optical cables has an optical amplifier (412, 414). The arrangement enables the interrogator to be remote from the array, for example 150 km or more, obviating the need for significant power to be supplied at the array.